Red Oak is a city in Ellis County, Texas, United States. The population was 4,301 at the 2000 census. More recent estimates of the city's population give it as 6,200. According to the United States Census Bureau, the city has a total area of 7.8 square miles (20Square kilometers), all of it land.The city of Red Oak is served by the Red Oak Independent School District. Acorn Academy, Shields Elementary, Eastridge Elementary, Red Oak Elementary, Wooden Elementary. Red Oak Intermediate School, Red Oak Junior High, Life School of Red Oak, and Red Oak High School.